Field of Invention
The invention relates to a rotor blade of a wind turbine, having a profile that has a suction side and a pressure side, wherein the profile comprises a camber line and a chord between a leading edge and a trailing edge of the profile, wherein the camber line extends at least portionally beneath the chord, in the direction of the pressure side, and wherein the profile has a relative profile thickness of more than 45%.
Brief Description of Related Art
Known from DE 10 2008 003 411 A1 are a rotor blade of a wind turbine and a corresponding family, or a plurality, of profiles. The airfoil profiles, or profiles, disclosed in this document have a blunt trailing edge, a substantially oval suction side and a substantially S-shaped pressure side.
Other profiles are also known. In particular, there are known low-speed profiles, which are used in proximity to the rotor-blade root, or in proximity to the hub of the wind turbine.
A profile of large relative thickness, known from Dieter Althaus “Niedriggeschwindigkeitsprofile”, Friedr. Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig/Wiesbaden, 1996, is produced in that a profile of small relative thickness, known per se, is brought to the required relative thickness values that are needed in the proximity of the blade root by truncating the trailing edge, or by scaling-up the thickness. An example that may be cited in connection with this is that of FX 77-W-500, which is disclosed on pages 162 to 163 of the book mentioned. This profile, in the clean state, in the case of a Reynolds number of 2.75 million, achieves a maximum lift coefficient of cl=1.6 with an angle of attack of 10°, and in the dirty, i.e. turbulent, state, achieves a maximum cl of 0.8 with an angle of attack of 4°. The FX 77-W-500 has a relative profile thickness of 50%.
In the context of the invention, an angle of attack, or angle of incident flow, is an angle of the incident apparent wind in relation to the chord of the profile. For any definitions, reference is to be made, in particular to the textbook: Erich Hau, “Windkraftanlagen”, Fourth Edition, 2008, in particular page 126 ff.
Although known profiles having a large relative profile thickness, such as, for example, the FX 77-W-500, do have an acceptable lift coefficient cl in the clean state, nevertheless in the case of turbulent circumfluent flow, i.e. in the dirty state, the maximum lift coefficient collapses significantly. In addition, the aerodynamic angle of attack at which the maximum lift coefficient is attained in the dirty state changes significantly in comparison with the angle of attack at which the maximum lift coefficient is attained in the clean state. This behavior, namely, the small amount of lift in the dirty state with a large change in the angle of attack for the maximum lift coefficient, is highly unfavorable for wind turbines. If, because the blade depths are to be kept small, the angle at which the clean profile has the maximum appropriate lift coefficient, or a lesser angle, is selected as the design angle of attack, i.e. the angle of attack that is used, in the design of the rotor blade, for calculating the respective profile, the lift coefficient in the dirty state then diminishes to a fraction of the clean value. Owing to the thick trailing edge, the profile of the FX 83-W-500 has only moderate aerodynamic properties even in the case of laminar circumfluent flow. In the case of turbulent circumfluent flow, it still has high lift coefficients, but then has relatively poor lift/drag ratios. Moreover, the maximum thickness of this profile is approximately 80% of the profile length, or chord length, which structurally does little to provide the rotor blade with a good body contour. Consequently, in the case of a blade having the profile of the FX 83-W-500, only a relatively small spacing of the main girders can be established, and this results in corresponding curtailments in respect of the constructability and blade weight of a rotor blade.
EP 1 944 505 B1 discloses a wind-turbine rotor blade having a profile that has a suction side and a pressure side, wherein the profile comprises an inner profile portion and an outer profile portion, wherein the inner profile portion is comparatively thicker than the outer profile portion, wherein the thickness of the inner profile portion is between 30% and 80% of the chord length of the inner profile portion, and the inner profile portion is provided with eddy generators, wherein the eddy generators are disposed, on the suction side of the inner profile portion, at between 8% and 12% of the chord length, as measured out from the leading edge of the profile portion. This is intended to achieve an adequate aerodynamic capability with, at the same time, a high structural stability.
The applicant's document DE 10 2008 052 858 A1 discloses particular profiles of a rotor blade, and a corresponding rotor blade of a wind turbine, in which the profiles provide very good aerodynamic properties. In particular, the profiles are relatively thick, and have a high lift coefficient. In order to achieve even higher lift coefficients for rotor blades of wind turbines, it might be possible to implement a measure used in the case of airfoils of aircraft. Thus, for example, the publication “Fluid-dynamic lift”, Information on Lift and its Derivatives, in Air and in Water, presented by Dr.-Ing. S. F. Hoerner 1985, pages 5-12 and 5-13, and also 6-2 and 6-3, Hoerner Fluid Dynamics, Bakersfield, Calif. 93390, disclose very high lift coefficients. In this case, high lift coefficients, of up to over 3.0, are achieved by the provision of flaps, in particular slotted flaps, adjoining the airfoil, and of flaps, in particular slotted flaps, projecting from the airfoil, which in each case are spaced apart from the actual airfoil.
It is the object of the present invention to specify a rotor blade of a wind turbine that has a very large lift, while having good aerodynamic properties.